Recent developments in computer technology have increased the storage capacity of media storage devices (e.g., hard disks, CD-ROMs, etc.) and have simultaneously increased the volatile memory storage capacity and data processing speeds of computer systems. These developments have facilitated using the computer system for processing and playback of signals representing motion pictures with associated sound recordings and other audio/visual multimedia recordings. An audio/video signal format has arisen called the Motion Picture Expert Group or MPEG format. The well known MPEG format, as described in international specifications ISO/IEC 11172-1 to ISO/IEC 11172-3, et seq., provides compressed and encoded digital audio and video signals from separate sources for data decompression and playback on computer systems. Specifically, the MPEG format offers an effective mechanism for intelligently compressing and decompressing digital video and audio signals and providing the decompressed signals to a playback mechanism.
In the past, most digitally recorded audio and video data signal formats interleaved the audio and video data in a single signal. In an interleaved format, the audio signal corresponding to the video frame signal is positioned adjacent and in sequence with the video frame signal on the recorded media. In older audio/video signal formats, the audio and video data were also provided from the source in the same frame sequence that was used for playback.
These prior art video and audio display formats, due to the above characteristics, did not pose any special problems with regard to audio and video signal synchronization during playback. For instance, if the audio and the video data signals were interleaved, then the audio and video synchronization information is effectively pre-recorded by the position of the interleaved audio and video signals on the storage media. With an interleaved audio and video signal format, the playback system merely presents the audio and video signals to the rendering equipment in the order they were received without any special synchronization issues. In an audio and video signal format that receives information in sequence, it is also relatively simple to synchronize the audio and video signals because they typically are never more than one frame out of synchronization.
However, the MPEG encodes the audio and video digital signals in an intelligent manner which poses synchronization problems during playback. For instance, MPEG signals are provided in individual defined digital data packets for both audio and video data. The digital data packets are not provided to the playback system in order relative to their playback sequence. Rather, the audio and video data packets are provided to the playback system out of playback order with an encoded system clock reference indicating the intended time of presentation for each audio and video data packet. Importantly, within the MPEG format, the audio and video digital data is not interleaved, but rather originates and is provided by separate sources. The above characteristics pose synchronization difficulties for computer systems that are required to properly playback the MPEG audio and video data signals in synchronization.
Accordingly, it is desired to provide a playback system (e.g., a computer system or dedicated digital playback system) with the ability to properly synchronize audio and video signals during playback that originate in a signal format that does not interleave the audio and video data and does not supply the audio and video data in a playback order sequence. It is further desired to provide a playback system as described above for proper playback of audio and video signals in an MPEG recorded format.